Brake system and a method for assembling thereof

ABSTRACT

A caliper for use in a disk brake system where a sufficient amount of grease exists at least in a space formed between a groove for setting a piston seal provided on the inside surface of the caliper body and a piston seal to be set therein, in a space formed between the outer surface of dust boots and said caliper body, and in a space formed by the dust boots, the caliper body, the piston and the piston seal; and a wheel cylinder for use in a drum brake system where a sufficient amount of grease exists at least in a space formed between a piston and a cup seal and in a space formed by the piston, a cylinder body and dust boots.

BACKGROUND OF THE INVENTION

[0001] 1) Field of the Invention

[0002] The present invention relates to a brake system, particularly,relates to a caliper for use in a hydrostatic disk brake system and awheel cylinder for use in a hydrostatic drum brake system, which areused in motor vehicles, airplanes, trains, etc. The present inventionalso relates to a method for assembling the caliper of a hydrostaticbrake system.

[0003] 2) Related Art Statement

[0004] Hydrostatic brake systems are generally used for the brakingsystems of motor vehicles, airplanes, or trains. The hydrostatic brakesystem is roughly classified into a disk brake system and a drum brakesystem. In either systems, a braking operation is carried out in such amanner that a brake master cylinder works to pressurize brake fluidcontained in the master cylinder responding to the braking operation byan operator, the pressure is transmitted to a caliper (disk brakesystem) or a wheel cylinder (drum brake system), and in the caliper orthe wheel cylinder, a piston works to effect the braking operation inaccordance with the pressure of the brake fluid.

[0005] During the braking operation, it is required that the piston isclosely adhered onto the inside wall of the cylinder in the caliper bodyin order to prevent a leakage of brake fluid and to realize a smoothmovement of the piston. Thus, in case of a disk brake system, a pistonseal is provided inside of a caliper, while, in case of a drum brakesystem, a piston cup is provided inside of a wheel cylinder. In a diskbrake system, a groove is provided inside of the cylinder of the caliperbody to hold the piston seal therein. While, there are two types of drumbrake system, one of which is a unified type where a groove is providedon an outer surface of the piston for holding the piston cup therein;the other one of which is a separated type where no groove is providedbut the piston cup is brought into contact with the outer surface of thepiston. The piston seal or the piston cup operates a pad or a lining viathe piston to generate a braking force when the pressure of the brakefluid is transmitted.

[0006] In assembling such a caliper or a wheel cylinder, a piston sealor a piston cup being treated with an oil material on the surfacethereof is used in order to make the assembling procedure easier. Theoperator sometimes uses grease to assemble the caliper or the wheelcylinder. However, the amount of grease used is very little and only forthe purpose of making the assembling procedure of the piston seal or thepiston cup into the caliper body or the cylinder body easy.

[0007] However, the caliper or the wheel cylinder assembled in theconventional manner has a problem as mentioned below.

[0008] In the conventional caliper for use in a disk brake system, whena brake pedal is stepped on to generate hydrostatic pressure, the pistonof the brake system is pushed as well as the piston seal, then thepiston seal is twisted. While, when the hydrostatic pressure isreleased, the twisted condition of the piston seal is retrieved so thatthe piston is aligned into its initial position by the self-aligningforce of the piston seal. In such a caliper, if the caliper is used fora long time, the contact portion between the piston and the piston sealbecomes not to work normally due to a variation of temperature of theoutside, a variation of temperature when vehicles are running, rust, ordust generated by the piston seal, so that the piston becomes not to bereturned properly. If the contacted portion between the piston and thepiston seal does not work normally, so-called shaking phenomenon of thepiston per se generates and such a movement of the piston may scratchthe inner surface of the cylinder. By such an abnormal movement of thepiston, so-called “brake drag” or a leakage of oil would be caused sothat the braking ability of the system would be decreased. Further, thedisk pad would be abraded so much by this “brake drag” phenomenon, agreat amount of dust is generated from the pads during the brakingoperation and the dust is sprinkled in an atmosphere. The dust gives anon-healthy influence to human bodies and once the dust adheres ontowheels, etc., it is very difficult to remove it.

[0009] The conventional wheel cylinder has the same problem. In theconventional wheel cylinder, since only a small amount of grease is usedfor assembling the piston cup into the wheel cylinder, if such a wheelcylinder is used for a long time, the piston operation would not workwell by a friction caused between the piston cup and the cylinder body.

SUMMARY OF THE INVENTION

[0010] The present invention is carried out in order to solve theabove-mentioned problem. The first aspect of the present invention is acaliper for use in a disk brake system, which comprises at least acaliper body having a cylinder portion, a piston, a piston seal and dustboots, said caliper body having a first groove for holding said pistonseal and a second groove for holding said dust boots, and said pistonhaving a third groove for holding said dust boots; wherein at least aspace formed between the first groove for positioning said piston seal,which is provided in an inside surface of the cylinder portion of saidcaliper body, and said piston seal being positioned in said firstgroove, a space between an outer side surface of said dust boots andsaid caliper body, in a space between an inner side surface of said dustboots and said piston, and a space formed by said dust boots, saidcaliper body, said piston and said piston seal, are filled with grease.

[0011] According to the first aspect of the present invention, out ofthe portions where the piston seal and the piston are made to contacttogether in the caliper of the disk brake system, the inside from thepiston seal would be covered by an oil film of a brake fluid, while, theoutside from the piston (the dust boots side) is covered by an oil filmof the grease. Therefore, it can be prevented that the temperature atthis contact portion becomes high or that the operation of the caliperbecomes out of order due to an impurity such as rust or dust, so that itbecomes possible to keep the movement of the piston seal and the pistonin the best condition for a long time. In this manner, in the caliperaccording to the present invention, the piston always works in a propercondition and therefore only the pressure of brake fluid transmittedfrom the master cylinder is properly applied to the contact portion ofthe piston and the piston seal so that the force of the piston istransmitted to the disk pad without generating any excessive force.

[0012] In the caliper of the disk brake system according to the presentinvention, it is preferred to provide another groove on the insidesurface of the cylinder of the caliper body between the first grooveformed in said caliper body for positioning said piston seal and thesecond groove for positioning said dust boots. Because, the grease isapt to be kept in the third groove, so that it becomes easy to hold thegrease in the really necessary portion, i.e. the space formed by thedust boots, the caliper body, the piston and the piston seal.

[0013] The present invention can be applied not only to a normal type(opposite piston type) of caliper but also to a floating type ofcaliper. In the floating type caliper, the caliper body is movablyinstalled with the aid of a pin, and a connecting portion for connectingthe caliper body and said pin is covered by dust boots. According to theinvention, it is required that a sufficient amount of grease exists in aspace formed by the dust boots and the pin, in a space formed betweenthe dust boots and an inner surface of a pin receiving section of thecaliper body, and in a space formed between an outer surface of the pinand the inner surface of the pin receiving section of the caliper body.

[0014] The second aspect of the present invention is a wheel cylinderfor use in a drum brake system which comprises at least a cylinder body,a piston which is to be positioned inside of said cylinder body, a cupseal provided between said cylinder body and said piston, dust boots forcovering said cylinder body and said piston, wherein at least a spaceformed between said piston and said cup seal and a space formed by saidpiston, said cylinder body and said dust boots are filled with grease.

[0015] In this manner, in the drum brake system, it also becomespossible to prevent an abnormal operation of the wheel cylinder byfilling the space between the piston and the cup seal, and the spaceformed by the piston, the cylinder body and the dust boots with grease,and thus the piston works in a stable manner for a long time.

[0016] Further, when assembling the caliper for use in a disk brakesystem, it is preferred that when installing the piston into the caliperbody, said grease is applied at least a half of the outer surface of thepiston from its inserting side, then penetrating the piston having thegrease on the half of the outer surface thereof into the caliper body(cylinder portion), so that the grease exists in the space formed by thedust boots, the caliper body, the piston and the piston sealsufficiently.

[0017] According to this assembling method, it becomes possible to put asufficient amount of grease in a desired portion, i.e. the space formedby the piston, the piston seal, the dust boots, very easily.

[0018] Furthermore, when assembling the caliper for use in a disk brakesystem, it is preferred that when installing the piston into thecylinder portion, after penetrating said piston into the cylinder fromthe top portion of the piston until the top portion reaches to thesequel of the piston seal, then extracting the piston once, and thenapplying the grease and penetrating the piston into the caliper bodyagain. By this operation, the initial fitting of the piston and thepiston seal becomes better.

[0019] It should be noted that if the operation of penetrating andextracting the piston is repeated, applying some grease on the surfaceof the piston, the fitting of the piston and the piston seal becomesmuch better and a sufficient and proper amount of grease can exist inthe desired space easily.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a cross-sectional view partially showing a caliper foruse in a disk brake system according to a first embodiment of thepresent invention:

[0021]FIG. 2 is a cross-sectional view partially depicting a wheelcylinder for use in a drum brake system according to a second embodimentof the present invention:

[0022]FIG. 3 is a cross-sectional view partially illustrating a caliperfor use in a disk brake system according to a variation of the firstembodiment shown in FIG. 1:

[0023]FIG. 4 is a cross-sectional view partially representing a caliperfor use in a disk brake system according to another variation of thefirst embodiment shown in FIG. 1:

[0024]FIG. 5 is a cross-sectional view partially showing a floating typeof a caliper for use in a disk brake system according to the presentinvention:

[0025]FIG. 6 is a graph showing an experimental result where the amountof “brake drag” generated in a brake system having a conventionalcaliper and that in a brake system having a caliper according to theinvention are compared: and

[0026]FIG. 7 is another graph depicting an experimental result where theamount of “brake drag” generated in a brake system is compared beforeand after the repairing according to the invention was conducted.

DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS

[0027] Preferred embodiments of the present invention will be explainedbelow on the basis of the attached drawings.

[0028]FIG. 1 is a cross-sectional view showing a construction of thefirst embodiment of the present invention where a caliper for use in adisk brake system is partially illustrated. In FIG. 1, the numericalreference 1 denotes a caliper body, 2 a piston, 3 a piston seal, 4 dustboots. The caliper body 1 comprises a cylinder portion 1 a, and in thecylinder portion 1 a, is provided a first groove 1 b for assembling thepiston seal 3. in the caliper body 1 is further provided a second groove1 c for setting the dust boots 4, while, on the outer surface of thepiston 2, is provided a third groove 2 a, which is opposite to saidfirst groove 1 a, for setting the dust boots 4 therein.

[0029] As shown in FIG. 1, according to the first embodiment, asufficient amount of grease is provided in a space S1, which is formedbetween the inner surface of the groove 1 b formed in the caliperportion 1 a for setting the piston seal 3 and the outer surface of thepiston seal 3, which is opposite to the inner surface of the firstgroove 1 b; in a space S2 formed between the outer surface 4 a of thedust boots 4 and the inner surface of the second groove 1 b formed inthe caliper body 1 for setting the dust boots 4; in a space S3 formedbetween the inner surface 4 b of the dust boots 4 and the groove 2 aformed in the piston 2 for installing the dust boots 4; and in a spaceS4 formed by a concave portion 4 c of the dust boots 4, which ispositioned on a piston seal side of the boots, a part of the caliperbody 1, a part of the inner surface of the piston 2, and a part of thesurfaces of the piston seal 3, which is positioned on the dust boots 4side.

[0030] It should be noted that the grease also exists on a contactsurface between the dust boots 4 and the piston 3 and on a contactsurface between the dust boots 4 and the caliper body 1 by putting asufficient amount of grease in the spaces S2 and S3.

[0031] By the existence of the grease in these spaces, the inner side(dust boots side) of the piston seal 3 is filled with grease, on theother hand, the outer side of the dust boots 4 is filled with brakefluid, so that the movement of the piston seal 3 becomes smooth and ashaking phenomenon of the piston 2 can be prevented. Further, since norust or no dust is generated inside of the caliper, the movement of thepiston in the caliper becomes extremely stable, so that so-called “brakedrag” of the brake system as a whole can be prevented.

[0032] The same effect can be obtained in the drum brake system.

[0033]FIG. 2 is a cross-sectional view showing a construction of thesecond embodiment of the present invention where a wheel cylinder foruse in a drum brake system is partially illustrated.

[0034] In FIG. 2, the numerical reference 11 represents a cylinder body,12 a piston, 13 a cup seal, 14 dust boots. In this embodiment, a groove12 a is provided in the piston 12 for setting a cup seal 13 there. Asshown in FIG. 2, a sufficient amount of grease exists in a space S5formed between the groove 12 a in the piston 12 and the cup seal 13 andin the space S6 formed by a part of the inner surface of the cylinderbody 11, a part of the outer surface of the piston 12 and the dust boots14.

[0035] According to this arrangement, the inside from the cup seal 13 inthe cylinder body 11 is filled with the grease and outside from the cupseal 13 with brake fluid. Therefore, the piston 12 is always broughtinto contact with the grease or the brake fluid, so that the pistonwould never shake even if it has been used for a long time. Further, norust or no dust is generated in the cylinder so that the normaloperation of the wheel cylinder can be kept for a long time.

[0036] In the second embodiment shown in FIG. 2, a wheel cylinder havinga groove provided in the outer surface of the piston is explained.However, it should be noted that the same effect can be obtained in aseparate type wheel cylinder where no groove is provided in the pistonbut a cup seal is just put between the piston and the cylinder body.

[0037]FIG. 3 is a cross sectional view showing a construction of thevariation of the first embodiment of the present invention, where acaliper for use in a disk brake system is partially represented. Itshould be noted that the same reference numbers are used for the sameelements in FIG. 1 and the explanation thereof is omitted here.

[0038] In the caliper shown in FIG. 3, the corner 1 a of the groove 1 bformed in the caliper body 1 for setting piston seal 3 is latched on thedust boots side. The arrangement of the latch portion Id makes it easierto put the grease in the space S4, which is necessary to be filled withthe grease.

[0039]FIG. 4 is a cross-sectional view depicting another variation ofthe caliper. In this variation, another groove 1 e is provided in theinner surface of the caliper body 1 between the groove 1 b for settingpiston seal 3 and the groove 1 c for holding the dust boots 4. As thesame as the variation shown in FIG. 3, by the arrangement of the groove1 e, the grease is apt to be easily collected there, so that the purposeof the present invention can be realized more easily. In this variation,the concave portion has a half-circled cross-section, but the shape ofthe groove 1 e is not limited to this variation.

[0040]FIG. 5 is a cross-sectional view illustrating a part of a floatingtype of a caliper, at which the caliper is installed with the aid of apin 5 so as to be slid back and forth. As shown in FIG. 5, a portion ofthe pin 5 protruded from the caliper body 1 is covered by dust boots 6having a bellows section. In such a type of caliper, it is preferred toput a sufficient amount of grease in a space S7 formed between the boots6 and the pin 5, in a space S8 formed between the outer surface of theboots 6 and the inner surface If of caliper body 1, and in a space S9formed between the outer surface of the pin 5 and the inner surface 1 fof the caliper body 1. Some kind of a floating type caliper uses arubber material (not shown) between the pin 5 and caliper body 6. Insuch a case, it is requested to apply the grease between the caliperbody 1 and the rubber material.

[0041] The method for assembling the caliper for use in a disk brakesystem according to the invention will be explained.

[0042] First, on the whole inside surface of the groove 1 b of thecaliper body 1 for setting a piston seal 3 and on the whole outersurface of the piston seal 3, is applied grease uniformly withoutexception, and the piston seal 3 is installed in the groove 1 a. By theexistence of grease between the groove 1 b and the piston seal 3, theadherence of the piston seal 3 in the groove 1 a becomes high, so thatthe movement of the piston seal 3 during the braking operation becomessmooth.

[0043] When the piston seal 3 is set into the piston seal groove 1 b,the level of the inner surface of the piston seal 3 becomes higher thanthat of the inner surface of the disk caliper 1 (the surface of thecylinder portion 1 a), so that a step is formed there. Then greaseshould be further applied around the piston seal 3 so as to bury thestep with the grease.

[0044] Next, grease is applied on the outer surface of the piston fromits top end (the end on the insertion side of the piston when insertingthe piston into the caliper body 1) to almost half of the piston as awhole; then the top portion of the piston 2 is inserted into the caliperbody 1 until the position some distant from the inner end 3 a of thepiston seal 3 (about 5 to 10 mm from the end 3 a), and then extractingthe piston once. At this time, since the grease is removed from the topend of the piston and adheres onto the inner surface of the caliper body1 and the piston seal 3, grease should be applied to the top halfportion of the piston again. Repeating the operation several times, andthen settle the piston into the caliper body 1 finally. By thisoperation, the grease applied on the top half of the piston is urgedagainst the upper side (dust boots side) of the piston seal 3; wheninserting the piston as a whole into the caliper body, a sufficientamount of the grease would exists at the upper side (dust boots side) ofthe piston seal 3. By repeating the operation, the initial fitting ofthe piston and the caliper body 1 becomes good.

[0045] Next, on the outer and inner side surfaces 4 a and 4 b of thedust boots (surface 4 b opposite to the groove 2 a formed in the piston2 and surface 4 a opposite to the groove 1 c formed in the caliper body1), and inside of the concave portion 4 c of the dust boots 4 on thepiston seal side, is applied a sufficient amount of grease, then settlethe dust boots 4 in the groove 1 b of the caliper body 1 and in thegroove 2 a of the piston 2. It should be noted that in case of usingdust boots having no concave portion 4 c, a sufficient amount of greaseshould be applied on the surface of the dust boots on the piston sealside.

[0046] By assembling the caliper in the above-mentioned manner, greasepervades over the portions which should have sufficient grease in orderto realize a smooth movement of the piston 2 and the piston seal 3during when the braking operation is conducted. According to thearrangement of the caliper mentioned above, the shaking of the pistonand the “brake drag” caused by the abnormal returning operation of thepiston can be prevented.

[0047] Any kind of grease for use in assembling or overhauling vehiclescan be used to conduct the present invention. However, according to theinventor's experience, it is proved that a better effect can be obtainedby using the grease of NICHIMORY FX 2300 (product name) manufactured byNichimori of Osaka Dockyard Co., Ltd.

[0048] An experiment, in which the grease of NICHIMORY FX 2300 was usedto assemble, will be explained below. In the experiment, the grease isapplied by hand, but it may be possible to use a spray device instead.

[0049]FIG. 6 is a graph showing the degree of “brake drag”, comparingbrake systems using a conventional caliper and a caliper according tothe present invention. In FIG. 6, the period of use of the brake systemis mentioned on the horizontal axis and the degree of “brake drag”caused in the brake system is shown on the longitudinal axis: the line Afor Example 1 shows how much “brake drag” was caused in the disk brakesystem where a conventional caliper is used. The line A proves that thedegree of “brake drag” becomes greater as the period of use of the brakesystem is increased. The line B for Example 2 shows a case that a newlymanufactured vehicle was be used until 4 and half year, then the caliperof the brake system of the vehicle was repaired applying the methodaccording to the present invention. That is to say, when repairing thebrake system, a sufficient amount of the grease of NICHIMORY FX2300 wasput in the spaces, which should be filled with the grease. The line Bproves that the degree of “brake drag” is largely decreased after therepairing. The line C for Example 3 shows the case that the caliperaccording to the present invention was used when the vehicle was newlymanufactured, where the grease of NICHIMORY FX2300 exists in the spaceswhich are required to be filled with grease to realize the effect of thepresent invention. It is apparent from the line C that the degree of“brake drag” was not aggravated even when seven years has passed afterthe vehicle had begun to be used.

[0050]FIG. 7 is a graph comparing the degrees of “brake drag” in sixsamples of motor vehicle manufactured by different motor vehiclemanufacturing companies; the caliper of each of the motor vehicles wasrepaired using the method according to the present invention so as toput NICHIMORIY FX2300 grease in the necessary spaces, some years afterthe vehicles had begun to be used; the degrees of “brake drag” beforeand after the repair are compared. The graph in FIG. 7 proves that thedegree of “brake drag” is improved after the repair irrespective of themanufacturer of the vehicles.

[0051] In the above-mentioned embodiments, the floating type caliper andreading trailing type wheel cylinder are explained; however, the presentinvention can also be applied to the other type of caliper, i.e. afloating yoke type caliper or a fixed type caliper, and to the othertype of wheel cylinder, i.e. the two reading type of wheel cylinder.

[0052] As explained above, in the caliper or the wheel cylinderaccording to the present invention, the reciprocal movement of thepiston is always conducted in a proper manner by the existence of greasein the necessary spaces. Therefore, the shaking phenomenon of the pistoncan be prevented and the “brake drag” is not caused for a long time.Further, since rust or dust is not apt to be generated in the cylinder,it can be prevented that the pads are abraded so that the powder of thepads becomes sprinkled to the outside. Furthermore, according to theinvention, since the friction can be restricted which is caused when thepiston seal (or cup seal) in the caliper (or in the cylinder) is slidbeing brought contact with the piston, the temperature in the caliper(the cylinder) and the temperature of the pads can always be kept low,so that the powder of the pads adhering on the disk can be washed outeasily by cold water.

What is claimed is:
 1. A caliper for use in a disk type brake systemcomprising at least a caliper body having a cylinder portion, a piston,a piston seal, and dust boots; said caliper body comprising a firstgroove for setting said piston seal and a second groove for setting saiddust boots, and said piston comprising a third groove for setting saiddust boots, wherein a sufficient amount of grease exists in a spaceformed by said first groove for setting said piston seal and said pistonseal attached around said piston, in a space formed by an outer sidesurface of said dust boots and said second groove formed in said caliperbody, in a space formed by an inner side surface of said dust boots andsaid third groove formed in said piston, and in a space formed by saiddust boots, said caliper body, said piston and said piston seal.
 2. Acaliper for use in a disk type brake system according to claim 1,wherein an edge portion on dust boots side of said first groove formedin said caliper body is latched.
 3. A caliper for use in a disk typebrake system according to claim 1, wherein said caliper body comprises afourth groove provided between said first groove and said second groove.4. A caliper for use in a disk type brake system according to claim 3,wherein said fourth groove has a semi-circular cross section.
 5. Acaliper for use in a disk type brake system according to any one ofclaims 1 to 3, wherein said grease also exists on a contact surfacebetween said dust boots and said piston and on a contact surface betweensaid dust boots and said caliper body.
 6. A caliper for use in a disktype brake system according to claim 1, wherein said caliper is arrangedas a floating type caliper where the caliper body is movably installedwith the aid of a pin, wherein said caliper body has a section forreceiving said pin and a part of the pin protruded from the caliper bodyis covered by another dust boots, and wherein a sufficient amount ofsaid grease also exists in a space formed by said another dust boots andsaid pin, in a space formed between said another dust boots and the pinreceiving section of said caliper body, and in a space formed between anouter surface of the pin and said pin receiving section of said caliperbody.
 7. A caliper for use in a disk type brake system according toclaim 6, wherein said dust boots has a bellows portion and a sufficientgrease exists in said bellows portion.
 8. A method for assembling acaliper for use in a disk type brake system, which comprises at least acaliper body, a cylinder, a piston, a piston seal, and dust boots,comprising the following steps when said piston is put into said caliperbody: a) applying grease to almost a half section of an outer surface ofsaid piston from an inserting end; b) pressing the piston having greaseon the half section thereof into said caliper body; thereby making saidgrease exist in a space formed by said dust boots, said caliper body,said piston and said piston seal.
 9. A method for assembling a caliperfor use in a disk type brake system according to claim 8, furthercomprising the following step when said piston is put into said caliperbody: c) retracting said piston from the caliper body once afterpressing the piston having grease on the half section into said caliperbody near the inside from an inner edge portion of said piston seal; d)applying said grease on the outer surface of said piston again; and e)pressing a whole part of said piston into said caliper body to settlethe piston finally.
 10. A method for assembling a caliper for use in adisk type brake system according to claim 9, wherein said piston ispressed into said caliper body after repeating said operations c) anda).
 11. A wheel cylinder for use in a drum type brake system at leastcomprising a cylinder body, a piston, a cup seal being provided betweensaid cylinder body and said piston, and dust boots for covering saidcylinder body and said piston, wherein a sufficient amount of greaseexists at least in a space formed between said piston and said cup seal,and in a space formed by said piston, said cylinder body, and said dustboots.